The present invention relates generally to rechargeable battery packs. More particularly, a modular battery design is disclosed that is particularly well suited for incorporation into large battery arrays having a multiplicity of battery units that are connected in both series and parallel.
With the increasing public concern over the pollution generated by fossil fuels, there have been extensive efforts to provide electrically powered automobiles. The principle limitation to the implementation of the electrically powered automobile is the lack of a suitable battery to serve as the energy storage device. Specifically, traditional battery designs have the dual drawbacks of being both quite expensive and quite heavy. In recent years, there have been substantial improvements in rechargeable battery technology. However existing battery designs remain quite heavy in comparison with other electrical components. The most common and probably best known battery construction is the lead acid battery. Substantially all of the existing automotive battery designs are lead acid based. One advantage of lead acid batteries is that they have very repeatable power delivery characteristics and may be recharged and overcharged repeatedly with minimal damage to the cells. Additionally, the power curve is consistent enough that the charge remaining in a cell at any given time can be relatively accurately predicted by merely measuring the cell's potential. Thus, a user can be easily warned well in advance of a loss of power. The major drawback of traditional lead acid batteries is that they tend to be heavy, and in order to ensure a reliable electrolytic seal between adjacent cells, it is generally necessary to form a gas tight seal about each cell.
A significant improvement in the traditional lead acid battery design was disclosed in U.S. Pat. No. 4,996,128 which described a recombinant lead acid battery having battery plates that are formed from metallic foils (i.e. lead and lead acid batteries). This arrangement permits the formation of multi-cell batteries. The multi-cell batteries may be incorporate dual function plate or be bipolar in nature to minimize weight. For example, in bipolar embodiments a single plate (foil) acts as a positive plate for one cell and a negative plate for an adjacent cell.
Since the weight characteristics of foil based lead acid batteries are substantially better than conventional lead acid batteries having large lead grids, enterprising individuals have produced very large scale battery arrays which combine large numbers of foil based lead-acid battery packs into a battery array. The array is arranged such that each battery pack unit (which may include a plurality of individual single cell battery packs) is coupled in parallel with a plurality of other battery pack units. These battery pack units that are connected in parallel effectively form a larger cell plane. The cell planes are then connected in series in order to form a battery array.
Although such an arrangement is quite advantageous when compared to the use of conventional lead acid batteries or batteries based on alternative chemistries, the connection between battery packs is relatively complicated. Accordingly, there is need for a lightweight battery construction which is particularly well suited for modular use in battery packs that connect individual units both in parallel with one or more adjacent battery units and in series with a separate group of adjacent battery units.